Traffic intersections may have multiple lanes of traffic moving in multiple directions, including passing through the intersection and turning at the intersection. Signalized traffic intersections help control these traffic movements in a safe and efficient manner by enabling a traffic signal to control the movements of traffic through the intersections.
A signal indication is one of the traffic lights at a signalized traffic intersection. The right-of-way, which enables a particular traffic movement to pass through the intersection or turn at the intersection, is assigned using the signal indications, where a green light indicates a right-of-way, and a red light indicates no right-of-way.
Traffic movements at an intersection have been standardized and designated with movement codes according to the National Electric Manufacturer's Association (NEMA). The individual traffic movements also are referred to as individual phases or vehicle phases herein.
In the conventional art, a phase is defined as any signal combination of one or more individual traffic movements that simultaneously receive the right-of-way. Herein, the terms “individual phase” and “vehicle phase” are distinguished from the term “phase.” The terms “individual phase” and “vehicle phase” herein are equivalent to an individual traffic movement as identified by the NEMA codes. Whereas, the term “phase” or “combination phase” as used herein means a combination of more than one traffic movement that simultaneously receive the right-of-way.
An example of the NEMA codes for the individual traffic movements or individual phases of an eight phase intersection is depicted in FIG. 1, where individual traffic movement 1 or individual phase 1 is the northbound left turn traffic movement. Individual phase 2 is the southbound through individual traffic movement. Individual phase 3 is the eastbound left turn individual traffic movement. Individual phase 4 is the westbound through individual traffic movement. Individual phase 5 is the southbound left turn individual traffic movement. Individual phase 6 is the northbound through individual traffic movement. Individual phase 7 is the westbound left turn individual traffic movement, and individual phase 8 is the eastbound through individual traffic movement.
Left turning traffic movements may occur in several different ways at various intersections. In one example, a left turn is not permitted. In another example, a left turn is permitted, but the left turn traffic must yield to opposing through traffic. In another example, a protected left turn occurs when an individual traffic movement is given a left turn green arrow signal. These are referred to as not permitted, permitted, and protected traffic movements.
A leading phase is a protected left turn individual traffic movement before an opposing traffic movement is released. For example, a northbound left turn traffic movement may be a protected left turn that leads coordinated northbound through and southbound through traffic movements.
A lagging phase is a protected left turn individual traffic movement after an opposing traffic movement is released. For example, the protected northbound left turn described above may be released after, and therefore lag, the coordinated northbound through and southbound through traffic movements.
An overlap includes a protected left turn traffic movement and a through traffic movement. For example, a northbound left turn overlap includes individual phases for a protected northbound left turn traffic movement and a northbound through traffic movement. Other examples exist.
When an intersection is signalized, a signal controller assembly controls the traffic movements at the traffic signal according to a timing plan. The timing plan identifies the order, start time, and duration of traffic movements at the intersection and prevents conflicting movements from having a right-of-way at the same time. For example, individual phase 2 and individual phase 3 conflict. Therefore, they could not both have the right-of-way at the same time.
Referring to FIGS. 2A-2B, in the conventional signal controller assembly, the timing plan has a cycle 202, which is a complete sequence of traffic movements for the intersection. The cycle 202 has a defined linear 204 order for each signal controller assembly. Therefore, each cycle 202 has a defined linear order of traffic movements.
Each cycle has a cycle length 206, which is the time it takes to complete one cycle with reference to a fixed point in the cycle. This fixed point sometimes is referred to as a yield point 208 and typically is the beginning or end of a main street green. Thus, the cycle length 206 is the time required to serve all individual phases at an intersection within a linear order with respect to the fixed reference point. This often is described in a short form as the time to serve a complete sequence of phases at an intersection. A cycle split is the percentage of cycle length allocated to one phase of a cycle. A phase split or individual phase split is the portion of the cycle length allocated to an individual phase. A signal phase or individual signal phase is a right of way for an individual phase.
As indicated above, a cycle has a predefined linear order of individual phases or combination phases with respect to a fixed point, sometimes referred to as a yield point. In the conventional signal controller assembly, the order in which the individual phases or combination phases are output are not changed from the linear order. One or more individual phases or combination phases may be skipped. Therefore, the sequence may appear to change in some instances. However, the linear order of the cycle does not change. If the controller assembly determines that a particular individual phase is to be generated, the signal controller assembly must first go through all the other phases in the linear cycle before reaching the particular individual phase that is to be generated. The interim phases may be skipped, thus appearing as if the linear order of the individual phases in the cycle has been changed or dynamically determined. However, it is only the pattern of the individual phases that has changed, not the linear order. The conventional systems emulate an analog mechanical cycle and do not select an order of states for a schedule or an order for signal phases for a timing plan.
Moreover, a conventional signal controller assembly cannot change the linear order of the individual phases in the cycle with respect to the fixed reference point. If the conventional signal controller assembly determines to generate a particular individual phase, it must wait until it reaches the point in the cycle where the individual phase can be served. If a signal controller assembly serves a first individual phase at a point in the cycle and then serves a second individual phase, it cannot again serve the first individual phase until the next cycle. Moreover, if the signal controller assembly serves all phases before the cycle length ends, it must wait until it reaches the fixed reference point to start a new cycle.
FIG. 2C illustrates a two ring architecture for serving an eight phase intersection. Ring one includes phases 1-4, and ring two includes phases 5-8. A barrier 210 exists as a safety mechanism to prevent interfering traffic movements. An individual phase on one side of the barrier 210 cannot receive a green light at the same time as an individual phase on the other side of the barrier. Additionally, once the barrier is crossed in the cycle, the signal controller assembly cannot serve any individual phase on the other side of the barrier again until the next cycle.
For example, multiple combinations of individual phases are generated for a timing plan in the cycle of FIGS. 2A-2B. In this example, individual phases 1 and 5 are generated, followed by individual phases 2 and 6, individual phases 3 and 7, and individual phases 4 and 8. The cycle 202 starts at the yield point 208, which is the beginning of the main street green, and the phases are output in the order identified in FIGS. 2A and 2B. A combination phase 1 and 6 may exist, but it is not identified in a timing plan for the cycle of FIG. 2. Similarly, the combination of individual phases 2 and 5 is not indicated in the cycle of FIG. 2. Thus, these combination phases are skipped. Therefore, it appears that the combination phases in the example of FIG. 2 are dynamically determined. However, the combination phase 2 and 6 cannot be generated as an output before the combination phase 1 and 5. Similarly, the combination phase 3 and 7 cannot be generated before the combination phase 2 and 6. Additionally, no combination of individual phases 1-2 and 5-6 can be served after the cycle crosses the barrier 210. Therefore, a true dynamic selection of individual phases or combination phases is not presented in the conventional signal controller assembly.
When multiple signal controller assemblies exist in a traffic network, the signal controller assemblies typically have a common cycle length. The cycles for each signal controller assembly are based on the fixed reference point. An offset between successive traffic signals is the time difference between the start of a green phase at an upstream intersection as related to the start of the green phase at an adjacent downstream intersection, which is determined from the fixed reference point. Therefore, each cycle in the traffic network is based on the fixed reference point.
Some traffic signal controller assemblies rely on a fixed timing plan that does not change. Other signal controller assemblies have a semi-actuated or fully actuated mode that enables the signal controller assembly to determine a timing plan based on traffic at the signal and traffic approaching the signal. Traffic waiting at the signal typically is identified using one or more types of detectors (also known as vehicle sensors), such as a loop detector, a puck (magnetic) detector, a video camera or other video detection device, a microwave detection device, and/or other detection devices. An example of a puck detector is the pavement mounted magneto-resistive sensor with wireless communication detection system from Sensys Networks. Traffic approaching the intersection may be identified by an upstream detector or a detector at an upstream intersection.
An example of such a conventional signal controller assembly is identified in FIG. 3. The signal controller assembly 302 of FIG. 3 includes a fixed mode, a semi-actuated mode, and a fully actuated mode. In the fixed mode, the signal controller assembly 302 executes a pre-determined timing plan. In the semi-actuated mode, the signal controller assembly 302 maintains a continuous right-of-way on a major street except when a demand is registered by a minor street detector. After the minor street is served, the right-of-way returns to the major street, such as when the detector on the minor street does not register any vehicles or a timing limit for the minor street has been reached. In the fully actuated mode, the signal controller assembly 302 measures traffic flow on all approaches to the intersection and makes assignments of the right-of-way in accordance with traffic demand. Detectors on the approaches to the intersection enable the signal controller assembly 302 to determine the single phases or combination phases to be generated in the timing plan to serve the major and minor streets. The fully actuated mode also is known as the “free” mode.
The semi-actuated and fully actuated modes are sometimes identified as adaptive control modes because the signal controller assembly 302 considers traffic flow when determining a timing plan. Therefore, the signal controller assembly 302 adapts to current conditions of traffic volume.
The signal controller assembly 302 includes an input/output (IO) board or interface 304 through which signals and/or communications are received or transmitted at or from the signal controller assembly 302. For example, signals identifying traffic volume approaching the intersection will be received by the signal controller assembly 302 through the IO board 304. A detector card 306 receives inputs from one or more detectors, such as detector 1 308 through detector N 310, where N represents a selected number of detectors at the intersection. For example, an intersection may have eight detectors, four detectors, or another number of detectors. The inputs from the detectors 308-310 to the detector card 306 are sometimes called detector calls, where one detector call represents the presence of at least one vehicle in a particular lane for an individual phase or individual traffic movement.
A controller unit 312 determines a timing plan and outputs the timing plan to the traffic signal 314 via the signal switches 316. The timing plan will vary depending on whether the signal controller assembly 302 is in the fixed mode, a semi-actuated mode, or the fully actuated mode. In addition, the timing plan will vary depending on whether detector calls are received from one or more detectors 308-310 corresponding to one or more individual phases. A conflict monitor (not shown) prevents traffic signal indications of conflicting traffic movements from being illuminated simultaneously to prevent hazardous conditions from occurring.
Even in the fully actuated mode, the cycle is constrained as being linear with a fixed reference point. The signal controller assembly cannot change the linear order of the cycle, i.e. the order in which individual phases or combination phases occur in its cycle. It can skip individual phases or combination phases in its timing plan, therefore changing the pattern in which the phases occur. However, the signal controller assembly 302 is limited by starting the cycle for the timing plan at the yield point and constraining the timing plan with the linear order of individual phases and combination phases in the cycle.
Moreover, multiple manufacturers of signal controller assemblies exist. While some commonalities occur between the various manufacturers, not all signal controller assemblies are manufactured the same way. Therefore, modifications made to one signal controller assembly type may not necessarily work for another signal controller assembly type. In addition, a processing system or other change to one type of signal controller assembly may not work for another type of signal controller assembly.
Several controller assemblies also have closed architectures so that the hardware and/or software cannot be changed by a traffic engineer. These include the NEMA TS-1 and the NEMA TS-2 standard models, whereas, the Caltrans 170 standard model has multiple hardware and/or software vendors without consistent hardware and software components. Further, current traffic controllers that are presently installed at intersections are not powerful enough to effectively run optimizations required by existing algorithms. Further, the conventional systems emulate an analog mechanical cycle and do not select an order of states for a schedule or an order for signal phases for a timing plan.